Die attach adhesive compositions

ABSTRACT

A novel thermally reworkable die attach adhesive composition for attaching a semiconductor device to a substrate is provided. The composition comprises 
     (a) a thermally reworkable crosslinked resin produced by reacting at least one dienophile having a functionality greater than one and at least one 2,5-dialkyl substituted furan-containing polymer, and 
     (b) at least one thermally and/or electrically conductive material present in an effective amount up to about 90% by weight of the die attach composition to provide a conducting medium.

This is a division of application Ser. No. 08/767,057 filed Dec. 16,1996, now U.S. Pat. No. 5,912,282 the entire disclosure of which ishereby incorporated by reference.

FIELD OF INVENTION

This invention relates to an adhesive composition. In one aspect, theinvention relates to die attach adhesive compositions suitable forattaching semiconductor devices to carrier substrates.

BACKGROUND OF THE INVENTION

Die attach adhesives are used to bond the semiconductor device such as asilicon die or chip to a substrate such as a lead frame or a printedcircuit board. During assembly of the semiconductor package, the dieattach adhesive holds the device firmly in place during wire bonding andencapsulation. They can provide electrical and/or thermal contactbetween the device and the substrate by means of incorporatingelectrically and/or thermally conductive fillers in the adhesiveformulation.

Examples of commonly used die attach adhesives are eutectic solders,conductive epoxies, and conductive polyimides. Eutectic solders aremetal alloys typically made with gold. A "preform", which is a metalfoil cut to the shape and size of the semiconductor chip, is depositedon the desired substrate of the package and is heated to a temperaturenear the melting point of the preform. The chip can then be placed ontothe preform with a scrubbing motion. The eutectic solders are expensiveand difficult to process. Conductive epoxies are typically low viscositypastes containing electrically conductive fillers. The epoxy is appliedto the substrate by conventional means and the device is then placed incontact with the coated substrate. The epoxy can then be cured in onestep. Conductive polyimides are similar to conductive epoxies.

Thermosetting die attach adhesives, primarily epoxy-based formulationsare used to bond semiconductor devices to substrates. Rework processesto replace defective chips usually involve the use of heat both beneaththe substrate and on top of the device accompanied by a shearing forceto remove the die from the substrate. Historically, rework has beenrelatively simple since the devices are small and widely spaced fromeach other. However, emerging packaging technologies such as multichipmodules use both larger devices and smaller spacing between them andtherefore raise the possibility of damage to the substrate duringrework. Thus, it is desirable to provide a die attach adhesivecomposition which allows the reworking to be more readily processable.

SUMMARY OF THE INVENTION

According to the invention, a thermally reworkable die attachcomposition is provided comprising:

(a) a thermally reworkable crosslinked resin produced by reacting atleast one dienophile having a functionality greater than one and atleast one 2,5-dialkyl substituted furan-containing polymer, and

(b) at least one thermally and/or electrically conductive materialpresent in an effective amount up to about 90% by weight of the dieattach composition to provide a conducting medium.

Such a die attach composition provides a readily reworkablesemiconductor board and/or semiconductor package.

DETAILED DESCRIPTION OF THE INVENTION

Thermally Reworkable Crosslinked Resin

There may be several ways by which the polymer chains of the thermallyreworkable crosslinked resin can be produced. The thermally reworkablecrosslinked resin can be produced by reacting at least one dienophilehaving a functionality greater than one and at least one 2,5-dialkylsubstituted furan-containing polymer connecting to one another viaDiels-Alder addition. In one embodiment the 2,5-dialkyl substitutedfuran groups are attached to or form part of the polymer chains.

The reversible furan to dienophile reaction to form the Diels-Alderadduct can be represented by: ##STR1## where Y is either C< or N--. Fora thermally reworkable crosslinked resin, all or a portion of theDiels-Alder adduct can revert to the furan and dienophile upon heatingsuch that the resin is a liquid (flowable material).

A crosslinking agent which contains in its molecular structure two ormore dienophiles can also be used in this embodiment. These dienophilesare connected to each other by chemical bonds or by bridging groups.Accordingly, the present invention also contemplates a die attachadhesive composition containing a polymer which comprises moieties of a2,5-dialkyl substituted furan and a crosslinking agent which comprisestwo or more dienophiles in its molecular structure. The dienophiles mayalso be attached to or form part of the polymer chains. Crosslinkingagent which comprises in its molecular structure two or more 2,5-dialkylsubstituted furan groups can also be used.

In yet another embodiment the dienophile is attached to the polymerchains to which the 2,5-dialkyl substituted furan groups are alsoattached or which contain the 2,5-dialkyl substituted furan groups as apart of their polymer chains. Accordingly, the 2,5-dialkyl substitutedfuran-containing polymer can also contain moieties of a 2,5-dialkylsubstituted furan and moieties of a dienophile.

The 2,5-dialkyl substituted furans may or may not be substituted attheir 3-and 4-positions. Preferred substituents are inert substituentssuch as for example alkyl or alkyloxy groups, typically having up to 10carbon atoms, such as methyl, ethyl, 1-propyl, methoxy and 1-hexyloxygroups. Resins containing furans whose 2 and 5 positions are notsubstituted are susceptible to side reactions which can causeirreversible gelling and interfere with its reversibility.

The 2,5-dialkyl substituted furan groups may be attached to the polymerchains of the polymer(s) on which the crosslinked resin is based. Theymay be attached thereto directly via a chemical bond or via a divalentorganic bridging group for which any of the substituents of the furansor the 3- or 4-positions of the furans may function as the point ofattachment. The alkyl substituents at the 2- and 5-positions of thefurans may be the same or different and will typically have up to 10carbon atoms. Examples of suitable alkyl groups are methyl, ethyl,2-propyl and 1-hexyl groups. Examples of suitable furyl groups which canbe attached to a polymer chain are 2,5-dimethylfur-3-yl,2,5-diethyl-3-methyl-fur4-yl, 5-ethylfurfuryl or 5-(1-butyl)furfurylgroups.

The type of polymer chains to which the 2,5-dialkyl substituted furangroups may be attached is not critical. Suitably the polymer chains arechains of a polyolefin, such as polyethene, polypropene, polystyrene,poly(acrylic acid) or a copolymer of ethene and acrylic acid or ester,chains of random or alternating copolymers of carbon monoxide andolefinically unsaturated compounds (for a further elaboration on suchcopolymers cf. hereinafter), or chains which contain heteroatoms, suchas chains of polyamide or polyester. It is preferred that the2,5-dialkyl substituted furans form a structural element of the polymerbackbone itself. In such a case it is particularly preferred that eachof the 2,5-dialkyl substituents of the furans are alkylene groups whichalso form part of the polymer chain and which may or may not besubstituted.

Such a structure can be produced by furanizing copolymers of carbonmonoxide and olefinically unsaturated compounds which contain1,4-dicarbonyl entities in their polymer chains, i.e. by converting such1,4-dicarbonyl entities into furan moieties. Alternatively, a2,5-dialkyl substituted furan-containing polymer can be directlyproduced by reacting carbon monoxide and olefinically unsaturatedcompounds in the presence of a strong acid.

Perfectly alternating copolymers of carbon monoxide and olefinicallyunsaturated compounds which contain 1,4-dicarbonyl entities in theirpolymer chains are known. They can be prepared by palladium catalyzedpolymerization using the methods known from, for example, EP-A-121965,EP-A-181014 and EP-A-516238. The polymers so prepared are alternatingcopolymers of carbon monoxide and the olefinically unsaturatedcompounds, i.e. copolymers of which the polymer chains contain themonomer units originating in carbon monoxide (i.e. carbonyl groups) andthe monomer units originating in the olefinically unsaturated compoundsin an alternating arrangement so that every fourth carbon atom of thepolymer chain belongs to a carbonyl group. Alternative copolymers ofcarbon monoxide and olefinically unsaturated compounds which contain1,4-dicarbonyl entities may be random copolymers, i.e. copolymers ofwhich the polymer chains contain monomer units in a random order. Thelatter copolymers can be prepared by radical initiated polymerizationusing the methods known from, e.g., U.S. Pat. No. 2,495,286 and U.S.Pat. No. 4,024,326.

The furanization of the copolymer of carbon monoxide and olefinicallyunsaturated compounds may be effected by methods known in the art, forexample, by applying phosphorus pentoxide as dehydrating agent, asdisclosed by A. Sen et al. (J. Polym. Science, Part A. Polym. Chem. 32(1994) p. 841), or by heating in the presence of a strong acid, such asp-toluenesulphonic acid, as disclosed in U.S. Pat. No. 3,979,373. Thesemethods allow the conversion of 1,4-dicarbonyl moieties in the polymerchains into furan moieties at a variable conversion level, dependingupon the reaction conditions selected.

It is preferred to employ in the furanization an alternating copolymerof carbon monoxide and olefinically unsaturated compounds because thesehave a higher content of 1,4-dicarbonyl groups in the polymer back-boneso that the furanization can be accomplished efficiently at a high levelof incorporation of furan groups. If, nevertheless, a low degree offuranization is desired, the conversion of carbonyl groups into furangroups may be kept low.

The copolymers of carbon monoxide and olefinically unsaturated compoundsmay be based on hydrocarbons as the olefinically unsaturated compounds.It is preferred that the copolymer is based on an olefinicallyunsaturated hydrocarbon, suitably an (α-olefin, in particular anα-olefin having up to 10 carbon atoms. Very suitable are aliphaticα-olefins, in particular those having from 3 to 6 carbon atoms and morein particular those having a straight carbon chain, such as propene,1-butene, 1-pentene and 1-hexene. Propene is most preferred. Thecopolymer can be regioregular or irregular, stereoregular or atactic.

A 2,5-dialkyl substituted furan-containing polymer where a polymer basedon propene and carbon monoxide are furanized can be represented by theformula: ##STR2##

The precise nature of the dienophile from which the Diels-Alder adductis obtained is not critical, as long as the Diels-Alder adduct has sucha thermal stability that the crosslinked resin is reworkable. Usuallythe minimum temperature above which the reworkable crosslinked resinwill be reworked depends on the maximum temperature requirements for thesemiconductor device used. The reworking is suitably carried out at atemperature from about 100° C., preferably from about 130° C., to about250° C., preferably to about 200° C.

Suitable dienophile functionality can be represented by Y═Y where Y iseither C< or N--, or --C.tbd.C--. Preferably the dienophiles are, forexample, alkynes having electron withdrawing groups attached to bothsides of the ethyne moiety, such as ester and keto groups. Examples aremono- and diesters of butynedioic acid (i.e. acetylenedicarboxylic acid)and substituted but-2-yne-1,4-diones. Other suitable dienophiles arecompounds which contain a but-2-ene-1,4-dione moiety included in a 5- or6-membered ring, in particular compounds of the general formula:##STR3## wherein X denotes O, S, N--, P-- or --R-- where R is alkylene,wherein at least one of the free valencies is occupied by a bridginggroup which connects the dienophile with one of the polymer chains orwith another dienophile, and wherein the remaining valencies, if any,are occupied by lower alkyl or acyl substituents or, preferably,hydrogen. The lower alkyl substituents suitably contain up to 4 carbonatoms and are, for example, methyl or ethyl groups. Dienophiles of thisgeneral formula are preferably cyclic derivatives of maleic anhydrideand, in particular, maleimide (i.e. X denotes O or, in particular, N--).

Examples of other suitable dienophiles include, bis(triazolinediones),bis(phthalazinediones), quinones, bis(tricyanoethylenes),bis(azodicarboxylates); diacrylates, maleate or fumarate polyesters,acetylenedicarboxylate polyesters.

As indicated hereinbefore, in one embodiment use is made of acrosslinking agent which comprises in its molecular structure two ormore dienophiles from which the Diels-Alder adducts are obtainable. Thedienophiles may be connected to each other by one or more bridginggroups. For example, three dienophiles may be connected to one anotherby a trivalent bridging group. However, it is sufficient that acrosslinking agent is used in which two dienophiles are connected to oneanother by a bivalent bridging group. The dienophiles may also beconnected to one another by chemical bonds.

Both the molecular weight and the chemical nature of the bridging groupof the crosslinking agent may be varied to a large extent. It has beenfound that such variations of the crosslinking agent lead to re-moldablecrosslinked resins covering a wide range of mechanical properties. Thebridging group may contain only carbon atoms in the bridge but it isalso possible that it contains heteroatoms in the bridge, such asoxygen, silicon or nitrogen atoms. The bridging group may be flexible orrigid.

For example, polymeric bridging groups having flexible polymer chains,such as poly(alkylene oxide) or polysiloxanes, having a number averagemolecular weight of, say, more than 300, provide rubbery reworkablecrosslinked resins. When the polymeric flexible chain has a numberaverage molecular weight in the order of 1500-5000 or more reworkablecrosslinked resins may be obtained which could replace thermoplasticrubbers.

Accordingly, suitable crosslinking agents of this kind are thebis-maleimido-capped poly(alkylene oxide)s, such as poly(ethyleneoxide)s or poly(propylene oxide)s, and bismaleimido-cappedpolysiloxanes, for example the bismaleimides of polysiloxanes of thegeneral formula H₂ N--CH₂ [--O--SiR₂ ]_(n) --O--CH₂ --NH₂, wherein n isan integer, on average, of more than 10 and in particular in the rangeof 20-70, and each R is independently an alkyl group, in particularhaving up to 5 carbon atoms, preferably a methyl group. Very goodresults can be obtained with the bismaleimide of bisamino cappedpoly(propene oxide), in particular having a number average molecularweight of at least 300, more in particular in the range of 1500-5000.

Low-molecular weight bridging groups, i.e. bridging groups whichtypically have up to 20 carbon atoms in the bridge, may also be used.Cycloaliphatic and aromatic bridging groups render the bridging groupsrigid. Low-molecular weight cycloaliphatic and aromatic bridging groupstend to provide re-moldable crosslinked resins which are hard andbrittle, and have a relatively high glass transition temperature.Examples of cycloaliphatic and aromatic low-molecular weight bridginggroups are groups containing a norbornane skeleton in the bridge,1,3-phenylene groups and groups of the following formulae: -f-CH₂ -f-,-f-O-f-O-f-, -f-O-f-SO₂ -f-O-f- and -f-C(CH₃)₂ -f-, wherein -f- denotesa 1,4-phenylene group. Other suitable bridging groups are alkylene andoxycarbonyl (ester) groups and combinations thereof. Suitablelow-molecular weight crosslinking agents are, for example, thebismaleimides of hydrazine, 2,4-diaminotoluene, hexamethylenediamine,dodecamethylenediamine, diamines of the general formula: ##STR4## andbisamino-capped (poly)siloxanes of low molecular weight, such aspolysiloxanes of the general formula H₂ N--CH₂ [--O--SiR₂ ]_(n) --O--CH₂--NH₂, wherein n ranges, on average, from 1 to 10, preferably from 1 to5 and the groups R are preferably methyl groups. An isomer mixture ofthe diamines of above formula is commercially available from HOECHST.Very good results can be obtained with bis(4-maleimidophenyl)methane anddimethylbis[(N-maleimidomethyl)oxy]silane.

Other suitable crosslinking agents on the basis of maleic anhydride arecompounds of the general formula: ##STR5## wherein A denotes a bridginggroup as described hereinbefore, in particular bridging group having upto 20 carbon atoms in the bridge. More in particular the bridging groupA is an alkylene group, such as a hexamethylene group, or groups-D-O-CO- or -CO-O-D-O-CO- wherein D denotes a bivalent hydrocarbylgroup, for example an alkylene group, such as a hexamethylene group.

Again other suitable crosslinking agents are polyesters based onbutynedioic acid and a diol, such as ethylene glycol, a poly(ethyleneglycol), propylene glycol or a poly(propylene glycol). These polyestersmay be low molecular weight crosslinking agents, such as describedhereinbefore, or they may have a number average molecular weight of, forexample, more than 400, such as in the range of 2000-6000.

The present invention also relates to crosslinking agents such asbis-maleimido-capped poly(alkylene oxide)s, in particularbismaleimido-capped poly(propene oxide)s. Such agents have a numberaverage molecular weight of at least 300, preferably in the range of1500-5000. The bismaleimides of polysiloxanes have the general formulaH₂ N--CH₂ [--O--SiR₂ ]_(n) --O--CH₂ --NH₂, wherein n is an integer of atleast 1 and each R is independently an alkyl group, in particular havingup to 5 carbon atoms, preferably a methyl group. The bismaleimido-cappedpolysiloxanes can be prepared by N-hydroxymethylation of maleimide withformaldehyde and subsequent reaction with the appropriatedichlorodialkylsilane in the presence of base and water using generallyknown methods.

As noted above, certain embodiments relate to a crosslinking agent whichcomprises in its molecular structure 2,5-dialkylfuran moieties. In thiscrosslinking agent the 2,5-dialkyl substituted furan groups can beconnected to one another via a chemical bond or via a bridging group.The nature of this bridging group is generally the same as the bridginggroup of the crosslinking agents which comprise two or more dienophiles,as described hereinbefore. Examples of suitable crosslinking agents arebis(5-ethylfurfuryl) adipate and the bis-amides of(5-ethylfurfuryl)acetic acid and the diamines mentioned in the precedingparagraphs.

The 2,5-dialkyl substituted furan moieties and/or moieties of adienophile may be connected to the polymer chains by means of a chemicalbond or by means of a bridging group. This bridging group may be of thesame type as the bridging groups of the crosslinking agents. Examplesmay be given as follows. When the polymer is a polystyrene, maleimide,as the dienophile, may be attached thereto by tin(IV)chloride catalyzedalkylation of the polystyrene with N-chloromethylmaleimide, and when thepolymer is a (styrene/maleic anhydride)copolymer a 5-ethylfurfuryl groupmay be attached thereto by esterifying the (styrene/maleicanhydride)copolymer with 5-ethylfurfuryl alcohol in pyridine. When thepolymer is a copolymer of carbon monoxide and olefinically unsaturatedcompounds which comprises 1,4-dicarbonyl entities in their polymerchains, 2,5-dialkylfurans and dienophiles may be attached thereto byreacting the copolymer with an appropriately substituted primaryhydrocarbylamine, e.g., using the methods known from U.S. Pat. No.3,979,374. In this reaction 1,4-dicarbonyl entities are converted intopyrrole entities which form part of the polymer chain and which areN-substituted with the substituted hydrocarbyl group. For example, acopolymer of carbon monoxide and olefinically unsaturated compoundswhich comprise 1,4-dicarbonyl entities may be reacted with themono-amide of maleic acid and hexamethylenediamine or with themono-amide of maleic acid and bis(4-aminophenyl)methane, followed byring closure of the acid-amido moieties to maleimide moieties. This willyield a polymer having N-(6-maleimidohexyl)pyrrole orN-{4-[(4'-maleimidophenyl)methyl]phenyl}pyrrole entities in the polymerchain. When it is desired to use a polymer which contains 2,5-dialkylsubstituted furan moieties and moieties of a dienophile a portion of the1,4-dicarbonyl entities of a copolymer-of carbon monoxide andolefinically unsaturated compounds may be converted into furan moietiesand another portion of the 1,4-dicarbonyl entities may be converted intoN-substituted pyrrole entities, of which the N-substituent comprise adienophile.

The molecular weight of the polymer(s) on which the reworkablecrosslinked resin is/are based may vary between wide limits. Suitablythe polymer(s) have a number average molecular weight within the rangeof at least 500, preferably 700, to about 30,000, preferably to about20,000.

The quantity of Diels-Alder adducts present in the thermally reworkablecrosslinked resin depends on the quantity of 2,5-dialkyl furan groupsand the quantity of the dienophile present in the composition from whichthe Diels-Alder adducts are formed. One skilled in the art willappreciate that a certain minimum quantity of Diels-Alder adducts isneeded to be present to effect that the crosslinked resin is a solidmaterial below the temperature at which the Diels-Alder adducts reverseto the 2,5-dialkyl substituted furan and the dienophile. It will also beappreciated that this minimum quantity depends on the molecular weightand the type of the polymer on which the resin is based and, if anycrosslinking agent is used, on the number of dienophiles or 2,5-dialkylfuran groups per molecule (i.e. functionality) of the crosslinkingagent. Lower molecular weights of the polymer will require a higherquantity of Diels-Alder adducts. The number of a Diels-Alder adducts maybe lower when a crosslinking agent is used which has a higherfunctionality.

Generally good results can be achieved by using the 2,5-dialkylfuran-containing polymer having a furan groups to ketone groups ratio offrom about 1:16 to about 4:1. The molar ratio of the 2,5-dialkylsubstituted furan groups to dienophiles amounts typically from about10:1 to about 1:5, preferably from about 5:1 to about 1:3.

CONDUCTIVE MATERIAL

In order to impart thermal or electrical conductivity to the adhesive,an effective amount of a thermally or electrically conducting materialis incorporated into the die attach adhesive composition. The preferredthermally conducting material are such as for example, beryllia, boronnitride, aluminum oxide (single crystal), aluminum nitride coated withcopper (see U.S. Pat. No. 5,288,769) and the like. Electrical contact isprovided by means of incorporating electrically conductive materials(fillers) such as silver, nickel, copper and aluminum particles as wellas alloys of such metals in the die attach adhesive formulation. Bothpowder and flake forms of conductive material may be used in the dieattach paste compositions. A preferred amount of thermally and/orelectrically conductive material ranges from about 60, preferably fromabout 70, to about 90, preferably to about 80 percent by weight of thetotal die attach adhesive composition, although lesser and greateramounts can be used.

DIE ATTACH ADHESIVES

Thermally reworkable die attach means that the device can be removedfrom a substate by liquefying the die attach composition (or adhesive)by heating. The die attach composition is liquefied when the compositionis flowable. The device can be removed without shearing or use ofexcessive force.

The thermally reworkable die attach composition of the inventioncontains (a) a thermally reworkable crosslinked resin produced byreacting a dienophile having a functionality greater than one and a2,5-dialkyl substituted furan-containing polymer, and (b) at least onethermally and/or electrically conductive material present in aneffective amount up to about 90% by weight of the die attach compositionto provide a conducting medium.

The thermally reworkable die attach composition can be worked and/orreworked at a temperature where the die attach composition melts.Typically, the thermally reworkable die attach adhesive can be workedand/or reworked at a temperature within the range from about 100° C.,preferably from about 130° C., to about 250° C., preferably to about200° C. If the composition is heated for an extended period of time athigh temperature, for instance, for 12 hours at 200° C., the compositionundergoes irreversible crosslinking and it is no longer thermallyreworkable.

The thermally reworkable die attach composition or adhesive can alsocontain other additives such as ion scavengers (e.g., tricalciumphosphate), free radical inhibitors (e.g., hydroquinone, phenothiazine),elastomeric modifiers (e.g., silicones), and other conventionaladditives used in die attach adhesives. For a longer reworking time, itis preferable to use ion scavengers and/or free radical inhibitors.

A process for attaching a semiconductor device to a substrate is alsoprovided comprising:

(a) providing the substrate;

(b) dispensing on the substrate a thermally reworkable die attachadhesive composition comprising

(i) a thermally reworkable crosslinked resin produced by reacting atleast one dienophile having a functionality of greater than one and atleast one 2,5-dialkyl substituted furan-containing polymer, and

(ii) at least one thermally and/or electrically conductive materialpresent in an effective amount up to about 90% by weight of the dieattach composition to provide a conducting medium, at a temperaturewhich is sufficiently high to convert the die attach adhesivecomposition into a liquid thereby producing an adhesive-attachedsubstrate, and

(c) attaching the semiconductor device on the surface of the thermallyreworkable die attach adhesive on the adhesive-attached substrate whilethe adhesive is a liquid, thereby bonding the semiconductor device tothe substrate and cooling the thermally reworkable die attach adhesiveto providing an assembly. The semiconductor device can be placed on theadhesive prior to substantial cooling by time or by heating to maintainor to reliquefy the adhesive to be a flowable material. The die attachcomposition can be dispensed on the substrate by using standardequipment such as a syringe or a motionless mixer that mixes thecomponents of the die attach composition and precisely dispenses thecomposition on the substrate.

Semiconductor devices can be bonded to various substrates such as forexample, various metal, ceramic or laminate substrates that includeprinted circuit boards (PCB) e.g., chip-on-board; to leadframes that arethen resin transfer molded into packages such as dual inline package(DIP) and plastic quad flat package (PQFP); and other packagingconfigurations such as ball grid array (BGA). Repair and rework ofdefective devices are becoming increasingly important for die attachadhesives. Multichip modules (MCM) use existing package technology withthe only difference being that a number of bare chips are adhesivelyattached to a substrate and packaged together. For instance, a BGAconfiguration might have a number of dies adhesively attached to asubstrate, tape automated bonding to make the connection from the die tothe substrate, an encapsulant coating all the dies as one package, andsolder balls that make the connection to the printed circuit substratefrom the BGA substrate. As spacing between the semiconductor device andnearby components such as other semiconductor devices gets closer,repair and rework without damage to adjacent devices becomes extremelydifficult. A thermally reworkable die attach adhesive of this inventionenables the user to perform repair and rework with ease on closelyspaced devices and high density substrates.

The thermally reworkable die attach adhesive composition bonded to asemiconductor device on one side and a substrate on another side can bereworked by steps comprising

(a) heating the die attach adhesive composition, said compositioncomprising

(i) a thermally reworkable crosslinked resin produced by reacting adienophile having a functionality greater than one and a 2,5-dialkylsubstituted furan-containing polymer, and

(ii) at least one thermally or electrically conductive material presentin an effective amount up to about 90% by weight of the die attachcomposition to provide a conducting medium, at a temperature which issufficiently high to convert the die attach adhesive composition into aliquid thereby providing a liquid die attach adhesive composition,

(b) removing the semiconductor device from the liquid die attachadhesive composition;

(c) optionally, dispensing a fresh thermally reworkable die attachadhesive composition, said composition comprising

(i) a thermally reworkable crosslinked resin produced by reacting adienophile having a functionality greater than one and a 2,5-dialkylsubstituted furan-containing polymer, and

(ii) at least one thermally or electrically conductive material presentin an effective amount up to about 90% by weight of the die attachcomposition to provide a conducting medium,

(d) optionally, providing another semiconductor device on the surface ofthe liquid die attach adhesive, thereby bonding another semiconductordevice on the die attach adhesive; and

(e) cooling the liquid die attach adhesive to a temperature which issufficiently low to solidify the resin.

The die attach adhesive composition can be postbaked to enhance the dieattach thermal and mechanical properties (e.g., glass transitiontemperature and mechanical strength). In order to preserve the thermalreworkability of the crosslinked resin, the die attach adhesive can beheated to a temperature within the range from about 70° C., preferablyfrom about 90° C., to about 200° C., preferably to about 160° C. for aperiod of time up to about 4 hours. If thermal reworkability is notrequired, the die attach adhesive composition can be postbaked at atemperature within the range of from about 150° C., preferably fromabout 180° C., to about 300° C., preferably to about 250° C. for aperiod of time up to about 4 hours to improve the thermal properties.

Illustrative Embodiment

The following illustrative embodiments describe the novel epoxy resincomposition of the invention and are provided for illustrative purposesand are not meant as limiting the invention.

EXAMPLE 1

An autoclave was charged with methanol and propene (approximately 2:1weight ratio), heated to 90° C., and then charged with carbon monoxideto a pressure of 72 bar. A catalyst solution of palladium acetate,1,3-bis(diethylphosphino)propane, trifluoromethane sulfonic acid, in aweight ratio of 0.6:0.62:1 and 0.3 pyridine, in a tetrahydrofuran andmethanol solution (15:1 volume ratio) were injected and the reactorpressure was maintained constant at 72 bar during the reaction by meansof a continuous supply of carbon monoxide. Removal of solvent yielded analternating propene/CO copolymer with a number average molecular weightof 733.

EXAMPLE 2

The alternating propene-CO copolymer with a number average molecularweight of 733 in Example 1 was dissolved in toluene and cyclized in thepresence of a catalytic amount of p-toluene sulfonic acid by heating atreflux. The resulting polymer was analyzed by C-13 NMR which showed that82% of the ketones in the starting polyketone were cyclized to furans(furan:ketone ratio 2.28:1) by the appearance of C-13 NMR signals (furanresonances) centered at around 107, 114, 147 and 153 ppm.

EXAMPLE 3

A system was made by blending the furanized polyketone made in Example 2and a stoichiometric amount of toluene diamine bismaleimide (CompimideResin TDAB, Technochemie Gmbh) at 340° F. The blend was removed from thegel plate and stored at room temperature. A solder-masked 8-ply(epoxy-glass) printed circuit board was placed on the gel plate at 340°F. and allowed to heat up to temperature. The blended system wasdispensed on the board and a silicon chip was placed on top of thesystem and allowed to adhere to the board. The board was removed fromthe gel plate and allowed to cool to room temperature. The die stayedadhesively attached to the board as the system formed a crosslinkedsolid at room temperature. The board was re-introduced back to the hotgel plate and allowed to heat for one minute. The chip was removed fromthe board easily as the adhesive system reverted back to itsuncrosslinked liquid state. The chip was reattached back on the board atits original location by means of the adhesive film that was stillpresent.

EXAMPLE 4

An alternating olefin-CO copolymer (27% ethylene, 73% propylene) with anumber average molecular weight of 1472 was prepared in a similar mannerto Example 1 from propene and ethylene. The copolymer was dissolved intoluene and cyclized in the presence of a catalytic amount of p-toluenesulfonic acid by heating at reflux. The resulting polymer was analyzedby C-13 NMR which showed that 56% of the ketones in the startingpolyketone were cyclized to furans (furan:ketone ratio 0.64:1).

EXAMPLE 5

A gel plate was set to 340° F. and the furanized polyketone made inExample 4 was dispensed onto the plate. A stoichiometric amount of TDABwas blended with the furanized polyketone until a homogeneous blend wasobtained. The blend was removed from the gel plate and stored at roomtemperature.

EXAMPLE 6

An ICI cone and plate viscometer was set to a temperature of 175° C. andallowed to equilibrate to the set point. A small amount of blend fromExample 5 was placed on the plate and allowed to come up to temperature.The cone was brought down and spun to obtain a good film between thecone and plate. This was verified by lifting the cone up to check forgood film formation. Subsequently the blend was allowed to equilibratefor 90 seconds and two viscosity readings were taken while the cone wasrotating at a fixed speed. The cone was lifted up and the blendretrieved from both the cone and plate. The blend was allowed to cool atroom temperature to a crosslinked solid. The above sequence of eventsi.e. load on ICI cone and plate, measure viscosity at 175° C., removeblend, cool to room temperature, was repeated three times with the sameblend. The three consecutive readings for viscosity were 3-5 poise, 3-5poise and 3-5 poise. This experiment shows that the blend can alternatereversibly between a crosslinked state at room temperature and a lowviscosity uncrosslinked liquid at 175° C.

EXAMPLE 7

An alternating propene-CO copolymer with a number average molecularweight of 1616 prepared in a similar manner to Example 1, except that1,3-bis(di-o-methoxyphenylphosphino)propane was used in the catalystsolution instead of 1,3-bis(diethylphosphino)propane. The copolymer wasdissolved in toluene and cyclized in the presence of a catalytic amountof p-toluene sulfonic acid by heating at reflux. The resulting polymerwas analyzed by C-13 NMR which showed that 57% of the ketones in thestarting polyketone were cyclized to furans (furan:ketone ratio 0.66:1).

EXAMPLE 8

A gel plate was set to 340° F. and the furanized polyketone made inExample 7 was dispensed onto the plate. A stoichiometric amount ofmethylene dianiline bismaleimide (Compimide Resin MDAB, TechnochemieGmbh) and 0.2 moles of phenothazine (Phenothiazine, Aldrich Chemical)per mole of MDAB was blended with the furanized polyketone until ahomogeneous blend was obtained. The blend was then removed and stored atroom temperature. A small portion of the blend was placed on the gelplate at 340° F. and mixed with 60% by weight of silver powder (Silverpowder, -325 mesh, Johnson Matthey). The components were mixed and theblend was then removed and stored at room temperature.

EXAMPLE 9

An ICI cone and plate viscometer was set to a temperature of 175° C. andallowed to equilibrate to the set point. A small amount of blend fromExample 8 was placed on the plate and allowed to come up to temperature.The cone was brought down and spun to obtain a good film between thecone and plate. This was verified by lifting the cone up to check forgood film formation. Subsequently the blend was allowed to equilibratefor 90 seconds and two viscosity readings were taken while the cone wasrotating at a fixed speed. The cone was lifted up and the blendretrieved from both the cone and plate. The blend was allowed to cool atroom temperature to a crosslinked solid. The above sequence of eventsi.e. load on ICI cone and plate, measure viscosity at 175° C., removeblend, cool to room temperature, was repeated three times with the sameblend. The three consecutive readings for viscosity were 70-75 poise,75-80 poise and 75-80 poise. This experiment shows that the blend canalternate between a crosslinked state at room temperature and anuncrosslinked liquid at 175° C.

EXAMPLE 10

A solder-masked 8-ply (epoxy-glass) printed circuit board was placed onthe gel plate at 340° F. and allowed to heat up to temperature. Thesilver-filled system of Example 8 was dispensed on the board and asilicon chip was placed on top of the system and allowed to adhere tothe board. The board was removed from the gel plate and allowed to coolto room temperature. The die stayed adhesively attached to the board asthe system formed a crosslinked solid at room temperature. The board wasre-introduced back to the hot gel plate and allowed to heat for oneminute. The chip was removed from the board easily as the adhesivesystem reverted back to its uncrosslinked liquid state. The chip wasreattached back on the board at its original location by means of theadhesive film that was still present and the board was removed from thegel plate and cooled to room temperature. This sequence was repeated twomore times i.e. place board back on hot surface, remove chip, reattachchip to board, cool to room temperature.

EXAMPLE 11

Furanized polyketone made in Example 7 and a stoichiometric amount ofTDAB along with 6.5% by weight of phenothiazine were heated to 1 80° C.,mixed and poured in a 1/8 inch thick metal mold. The mold was cooledquickly and the resulting 628 ksi, a value similar to that of acrosslinked epoxy made with bisphenol-A epoxy cured with an anhydridehardener. The dielectric constant and dissipation factor were 3.17 and0.013 respectively.

EXAMPLE 12

Furanized polyketone made in Example 7 was reacted with a 2:1stoichiometric ratio of MDAB, 0.1 mole of phenothiazine/mole of MDAB and0.015 gm of 2-ethyl hexanoic acid/gm of furanized polyketone. Adifferential scanning calorimetry scan was performed on the sample at aramp rate of 20° C./min. The onset of the glass transition temperatureoccured at 105° C.

EXAMPLE 13

Furanized polyketone made in Example 4 was reacted with a stoichiometricamount of TDAB and 0.1 moles of phenothiazine/mole of TDAB on a gelplate at 340° F. This sample was ground and placed in a Parr bomb withwater in a 10:1 ratio (water:sample). The Parr bomb was kept at 60° C.for 20 hours and the water extract was analyzed for ions by ionchromatography. The extract contained 14 ppm acetate, <3 ppm glycolate,formate, propionate, <0.25 ppm chlorine, <1 ppm nitrate, 1.7 ppmsulfate, 4.8 ppm sodium, 0.8 ppm magnesium, 2.5 ppm calcium and 0.2 ppmammonium ion.

We claim:
 1. A process for attaching a semiconductor device to asubstrate comprising:(a) providing a substrate; (b) dispensing, on atleast a portion of said substrate, a thermally reworkable die attachadhesive composition, said composition comprising(i) a thermallyreworkable crosslinked fesin produced by reacting at least onedienophile having a functionality greater than one and at least one2,5-dialkyl substituted furan-containing polymer, and (ii) at least onethermally and/or electrically conductive material present in aneffective amount up to about 90% by weight of the die attach compositionto provide a conducting medium, at a temperature which is sufficientlyhigh to convert the die attach adhesive composition into a liquidthereby producing an adhesive-attached substrate; (c) attaching thesemiconductor device on the surface of the thermally reworkable dieattach adhesive on the adhesive-attached substrate while the adhesive isin a liquid, thereby bonding the semiconductor device to the substrate;and, (d) cooling the die attach adhesive to a temperature which issufficiently low to solidify the resin thereby providing an assembly. 2.The process of claim 1 wherein the crosslinked resin is heated at atemperature within the range of from about 100° C. to about 250° C. 3.The process of claim 1 wherein the 2,5-dialkyl substitutedfuran-containing polymer is produced by reacting carbon monoxide with atleast one olefinically unstaturated compound.
 4. The process of claim 1wherein the dienophile is a cyclic derivative of maleic anhydride. 5.The process of claim 1 further comprising the step of (e) heating theassembly at a temperature within the range of 70° C. to 200° C. for aperiod of up to 4 hours.
 6. The process of claim 1 further comprisingthe step of (e) heating the assembly at a temperature within the rangeof 150° C. to 300° C. for a period of up to 4 hours.
 7. The process ofclaim 1 further comprising the steps of:(e) heating the thermallyreworkable die attach adhesive composition of the assembly at atemperature which is sufficiently high to convert the die attachadhesive composition into a liquid thereby providing a liquid die attachadhesive composition, (f) removing the semiconductor device from theliquid die attach adhesive composition; (g) optionally, dispensing afresh thermally reworkable die attach adhesive composition comprising(i)a thermally reworkable crosslinked resin produced by reacting adienophile having a functionality greater than one and a 2,5-dialkylsubstituted furan-containing polymer, and (ii) at least one thermally orelectrically conductive material present in an effective amount up toabout 90% by weight of the die attach composition to provide aconducting medium, (h) optionally, providing another semiconductordevice on the surface of the liquid die attach adhesive, thereby bondinganother semiconductor device on the die attach adhesive; and (i) coolingthe liquid die attach adhesive to a temperature which is sufficientlylow to solidify the resin thereby providing a reworked assembly.
 8. Theprocess of claim 7 wherein the crosslinked resin is heated at atemperature within the range of from about 100° C. to about 250° C. 9.The process of claim 7 wherein the 2,5-dialkyl substitutedfuran-containing polymer is produced by furanizing a copolymer of carbonmonoxide and at least one olefinically unsaturated compound.
 10. Theprocess of claim 9 wherein the dienophile is a cyclic derivative ofmaleic anhydride.